Mackenzie Crook looks more like a Bohemian artist than a Hollywood glamour boy but the Pirates of the Caribbean and Office star actor was pretty open about what it meant to him to talk about his first work of fiction, The Windvale Sprites, in front of a crowded theatre of children at the The Telegraph WordUp! Festival.

Crook, who is currently appearing in the hit play Jerusalem,said: "I love being on stage. And I have had a spell as a stand-up comedian. But when I was doing comedy, I was always doing characters so that was a bit of a disguise I could hide behind. But I have done nothing more nerve-racking than writing this book. It's there in black and white for everyone to judge. Broadway was a walk in the park compared to this."

The 40-year-old talked about the inspiration for his book - the idea first came to him after the great October storm of 1987. Crook has provided the illustrations and words for the book and, with the aid of a live camera and big screen, drew some illustrations as he talked. He praised the illustrators he admired, including Jill Bennett and Diane Stanley, the woman responsible for the brilliant Burrowers artwork. Crook said he loved "eerie, dark and sinister" illustrations in general.

He dealt well with a question rolled his way like a hand grenade about whether he had been able to get his book published only because he was famous. "It's not a celebrity book" he answered. Being an actor, he explained, did mean that he had lots of spare time and it was a matter of using that time productively. The audience seemed able to tell that he was talking about a book he genuinely believed in. He explained that he had written the book partly to entertain his son, now eight, who is Dyslexic.

The long question and answer session prompted one big laugh from the crowd when a child asked: "Is your son in the audience?"